Apparatus for photochemical reactions



Nov. 4, 1969 w, BEKMANN ETAL 3,476,669

APPARATUS FOR PHOTOCHEMICAL REACTIONS Filed April 6, 1966 FIG.3

FlG l FIG-4 FIG. 5

INVENTORSI WlLHELM BECKMANN WERNER LUDWIG KENGELBACH HORST METZGER MARTIN PAPE ATT'YS United States Patent 3,476,669 APPARATUS FOR PHOTOCHEMICAL REACTIONS Wilhelm Beckmann, Limburgerhof, Pfalz, and Werner Ludwig Kengelbach, Horst Metzger, and Martin Pape, Ludwigshafen (Rhine), Germany, assignors to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany Filed Apr. 6, 1966, Ser. No. 540,741 Claims priority, applicatioln germany, Apr. 9, 1965,

Int. Cl. B01k 1/00; C07c 3/24 US. Cl. 204193 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to apparatus for carrying out photochemical reactions in a reaction vessel filled with liquid with lamps dipping into the liquid.

In carrying out photochemical recations, dilficulties often arise because reaction products in solid or viscous form deposit on the light transmitting surface of the lamp which is in direct contact with the reaction liquid. This prevents transmission of the chemically active light and leads to a decrease in the light yield. It is therefore necessary either to make the formation of such deposits impossible from the start or to remove them Iby suitable devices and measures.

For example this may be achieved by cleaning the light transmitting surface continuously or intermittently with a film of liquid which will dissolve the obscuring layer and will not mix with the recation liquid, Another known method is to produce on the light transmitting surface a regeneratable, indifferent and light-permeable crystal layer. It is also known that the deposit may be removed mechanically by means of brushes moved manually or automatically.

All the prior art methods. have disadvantages because they either give no reliable protection against the formation of deposits or require expensive apparatus. These difficulties are much greater in a large plant in which not only one but several lamps are used at the same time.

We have now found that in such cases the light transmitting surface may be kept free from deposits for long periods by using an apparatus having a vessel filled with the reaction liquid and lamps, wherein stirring means is provided in the vessel and the lamps are arranged around the stirring means so that the clearance between the lamps is 0.3 times to twice the outer diameter of the lamps and the clearance between a lamp and the inner wall of the vessel is at least 0.5 times the diameter of the lamp and the clearance between the outer edge of the stirrer and a lamp is from 0.05 times to 0.5 times the diameter of the lamp. The lamp is regarded as the immersed unit consisting of the light surce proper, the cooling jacket and any outer protective tube which may be used.

When viewed in plan, the mid points of the lamps are arranged in a circle.

The lamps and stirring means are arranged vertically.

Some of the lamps may be replaced by cooling means having the same dimensions. For withdrawal of heat, the

wall of the vessel may be constructed as a cooling jacket. Cooling tubes may however be provided vertically or horizontally between the lamps and the Wall of the vessel.

To carry out photochemical reactions in a large plant, a number of units, each consisting of a stirrer and lamps located around the same, are arranged in series in a vessel and the vessel is subdivided by means of partitions provided with openings and located between the units to prevent backmixing.

For continuous reaction, a number of vessels may be arranged in series with cooling means between the vessels.

The apparatus in accordance with this invention may be used for example for preparing oximes from cycloalkanes; a solvent may be used if desired and stirring is effected at 40 to 200 r.p.m.

The apparatus according to this invention ensures that adequate turbulence is produced in the liquid over the entire exterior surface of the lamps, so that reaction liquid is uninterruptedly directed from the interior of the vessel to the light transmitting surfaces from the interior of the vessel to the light transmitting surfaces and away again, so that the formation of deposits is impossible. It is necessary that the clearances between the lamps should not be above or below certain limits. If the clearance is too small, it has been found by experiment that a zone with too little motion forms between the two lamps. If the clearance is too great, however, a flow shadow forms on the opposite side to the flow.

The distance from the outer wall should also be large enough to ensure complete absorption of the chemically active light in the gap between the lamp and the wall of the vessel and to ensure adequate movement of the liquid. The stirring means should be sufliciently large in diameter to ensure that the turbulence is effective throughout the reactor. On the other hand an adequate clearance between the edge of the stirrer and the lamps must be provided so that the lamps are not broken as a resu t of virbrations caused by too strong a load on the glass wall.

The invention will no be described with reference to the accompanying drawings in which appartus according to the invention are shown by way of example. I the drawings, FIGURES 1 and 2 show diagrammatically in side elevation and transverse section an apparatus having a disc impeller mixer, FIGURE 3 is a side elevation of an appartus having an anchor stirrer, FIGURE 4 is a crosssection of an apparatus having cooling means, FIGURE 5 is a plan view of an arrangement of several apparatus in a vessel having partitions, and FIGURE 6 shows diagrammatically a layout of vessels and coolers.

Referring to FIGURE 1, the apparatus according to the invention is installed in a reactor 1 filled with reaction liqiud. Lamps 2 having an external diameter D dip into the reactor 1. In this arrangement, the lamp may emit the chemically active light in all directions into the reaction liquid. A stirrer, for example a blade stirrer 3, is provided in the middle of the reactor 1. The lamps are located around the stirrer at regular intervals so that the clearance l between any two neighboring lamps is not less than 0.3D and not more than 2.0D Similarly, the clearance m between the lamps and the reactor wall should not be less than 0.5D.

The dimensions of the stirrer are chosen so that the clearance it between the outer edge of the stirrer and a lamp is from 005D to 0.5D. The speed of rotation of the stirrer should be high enough to ensure turbulent flow throughout the reactor. The stirrer should have a height at least equal to the light-emitting length of the lamp.

Electric current is supplied to the lamps through leads 4, 5. A motor 6 is provided which drives the shaft 7 of the stirrer. The stirrer may also take the form of an anchor stirrer (FIGURE 3) between the reactor wall and the lamps, the above clearances between the edge of the stirrer and the lamps being maintained.

To obtain a maximum and uniform clearing effect of the turbulent flow produced by the stirrer over the whole outer surface of the lamps, the direction in which the stirrer is rotated may be reversed at definite intervals determined by the liquid and the reactor. In this way the whole of the outer surface of the lamps is directly swept by the liquid at regular intervals. The same effect may also be achieved by making the lamps rotatable about their axes and carrying out a rotation of up to 180 after predetermined periods. For reliability and ease of operation, the lamps and stirrer are arranged vertically, In the case of apparatus which is not operated under pressure, the use of stufiing boxes may thus be avoided or they may be protected from direct contact with the reaction liquid which is often very corrosive.

Photochemical reactions may be exothermic. The reaction liquid may then become hot. As a result, reaction may be impaired or even completely inhibited. In this case it is necessary to install cooling means 8 (FIGURE 4) which prevent the heating up of the reaction liquid. These cooling means may replace some of the lamps and have the same geometrical dimensions as the lamps. The wall of the reactor 1 may however be designed as a cooling jacket 9, or horizontal or vertical cooling coils or cooling tubes 10 may be installed. In all cases excellent heat transfer is achieved because of the turbulent flow produced by the stirrer.

In the case of a large plant, a number of the abovementioned reaction vessels may be connected in series as shown in FIGURE by arranging them in a vessel 11 which may advantageously have an elongated rectangular shape, The individual reactors, each provided with stirring means 12, may be separated by partitions 14 provided with openings 13. Backmixing of the reaction liquid is thus avoided and a steady increase in the amount of reaction product is achieved in the direction of flow.

The series connection of individual reactors to a reaction system as shown in FIGURE 5 cannot be extended indefinitely, especially when installation of cooling units instead of individual lamps or the installation of cooling coils is to be dispensed with so as to make full use of the reaction chamber for the photosynthesis. In such cases an intermediate cooling may be provided if the rise in temperature of the reaction liquid exceeds the permissible limit. The arrangement may then be as shown in FIGURE 6 where the reaction liquid, after it has flowed through the first reaction system 15, is passed through a coolingunit 16, and then through a second reaction system 17 and cooling unit 18, and if desired through further reaction systems 19, 21, 23 and 25 between which are interposed cooling units 20, 22 and 24; final cooling is effected by cooling unit 26. This arrangement also has the advantage of a continuous build-up of the desired reaction product without troublesome backmixing.

We claim:

1. Apparatus for carrying out photochemical reactions comprising a vessel adapted to hold a reaction liquid, stirring means having rotating stirring members for agitating the reaction liquid in said vessel, and a plurality of lamps located in said vessel at positions relative to the stirring members so that the clearance between contiguous lamps is from 0.3 times to twice the diameter of a lamp, the clearance between respective lamps and the Wall of the reactor is at least 0.5 times the lamp diameter and the clearance between the edge of the stirring members and respective lamps is from 0.05 to 0.5 times the diameter of the respective lamp.

2. Apparatus as claimed in claim 1 wherein at least one of the lamps is replaced by a cooling means having the same dimensions.

3. Apparatus as claimed in claim 1 wherein the wall of the reactor is constructed as a cooling jacket.

4. Apparatus as claimed in claim 1 wherein cooling tubes are arranged vertically between the lamps and the wall of the reactor.

5. Apparatus for carrying out photochemical reactions as claimed in claim 1 wherein a plurality of units each comprising a stirring means and a number of lamps arranged around the same are arranged in a vessel and partitions having openings therein are provided between the units to prevent backmixing.

6. Apparatus as claimed in claim 1 comprising a plurality of said vessels containing said stirring means and said lamps, means for passing reaction liquid sequentially through said vessels, and cooling means for cooling reaction liquid as it passes between each pair of vessels.

7. Apparatus as claimed in claim 1 wherein said lamps are tubular lamps with respective vertical longitudinal axes and said stirring means comprises a vertical rotatably driven shaft with a plurality of vertically disposed stirring members connected to and rotatably driven by said shaft.

8. Apparatus as claimed in claim 7 wherein said lamps, as viewed in plan, are arranged in a circle concentrically about said shaft.

References Cited FOREIGN PATENTS 11/1964 France,

1/1966 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner 

